Hard disk drives are mass storage devices that include a magnetic storage media, e.g. rotating disks or platters, a spindle motor, read/write heads, an actuator, a pre-amplifier, a read channel, a write channel, a servo circuit, and control circuitry to control the operation of hard disk drive and to properly interface the hard disk drive to a host system or bus. FIG. 1 shows an example of a prior art disk drive mass storage system 10. Disk drive system 10 interfaces with and exchanges data with a host 32 during read and write operations. Disk drive system 10 includes a number of rotating platters 12 mounted on a base 14. The platters 12 are used to store data that is represented as magnetic transitions on the magnetic platters, with each platter 12 coupleable to a head 16 which transfers data to and from a preamplifier 26. The preamp 26 is coupled to a synchronously sampled data (SSD) channel 28 comprising a read channel and a write channel, and a control circuit 30. SSD channel 28 and control circuit 30 are used to process data being read from and written to platters 12, and to control the various operations of disk drive mass storage system 10. Host 32 exchanges digital data with control circuit 30.
Data is stored and retrieved from each side of the magnetic platters 12 by heads 16 which comprise a read head 18 and a write head 20 at the tip thereof. The conventional read head 18 and write head 20 comprise magneto-resistive heads adapted to read or write data from/to platters 12 when current is passed through them. Heads 16 are coupled to preamplifier 26 that serves as an interface between read/write heads 18/20 of disk/head assembly 10 and SSD channel 28. The preamp 26 provides amplification to the waveform data signals as needed.
The magnetic flux transitions on the magnetic platter 12 are created by switching the write current polarity through the write head 20. Conventionally, four transistors are connected to the write head 20 in a typical H-bridge arrangement in which the direction of current through the write head 20 is controlled by raising the on one node (this voltage level is referred to as the high side voltage) and lowering the voltage on the other node (this voltage level is referred to as the low side voltage). The current direction can be changed by raising the low side voltage such that it becomes the high side and lowering the high side voltage such that it become the low side. Changing the direction of the coil current changes the magnetic flux through the write head 20.
Power dissipation, stable voltage reference, self-heating effects and production costs are some of the major design concerns for coil drive circuitry and are particularly important as the switching speeds increase. For example, during operation, an amplifier circuit consumes current from a power supply in which a portion of this current, known as the quiescent current, is used to bias the internal circuitry of the amplifier. A low quiescent current is most desirable because it reduces power consumption when the amplifier is operable at a light load, or with no load at all. Further, a stable reference and reduced self-heating effects improves the overall performance of the drive circuit.
There is desired an improved high speed write coil driver circuit that improves high data rate operation with reduced power in a reduced cost process. This can be achieved by providing a stable reference with a high speed pre-drive and a fast main writer that operates at reduced power while enabling write operation at very high speed.